Structural Evolution and Thermoelectric Performance in (GeTe)m(Sb2Te3)n Compounds

Exploring the relationship between crystal structure and thermoelectric performance is a pivotal topic in the thermoelectric field. In this study, we have comprehensively investigated the correlation between the structural evolution of (GeTe)m(Sb2Te3)n pseudo-binary system and the thermoelectric properties. The proportion of van der Waals bonds increases with the rising Sb2Te3 content, resulting in an increase in the anisotropy of the electrical conductivity and a decrease in the average sound velocity. Additionally, the cation sites in the crystal lattice of these compounds exhibit a mixed occupancy of Ge/Sb atoms, although the cation sites adjacent to the van der Waals gaps are predominantly occupied by Sb atoms. The ultra-low lattice thermal conductivity of the GST124 and GST147 compounds is mainly attributed to the high concentration of van der Waals bonds and enhanced phonon scattering arising from Ge/Sb mixed cation occupancy and high density of defect structures. The high electrical conductivity combined with the low lattice thermal conductivity enables GST124 and GST147 compounds to achieve a maximum ZT value of 0.56 and 0.57, respectively. Higher thermoelectric performance can be achieved through optimization of the microstructure as well as the carrier concentration.